Mitigation of interference due to peer-to-peer communication

ABSTRACT

Techniques for mitigating interference due to peer-to-peer (P2P) communication are described. In an aspect, a P2P UE may measure the signal strength of downlink signals from base stations and may set its transmit power based on (e.g., proportional to) the measured signal strength in order to mitigate interference to WWAN UEs communicating with base stations. In another aspect, the P2P UE may measure the signal strength of uplink signals from WWAN UEs and may set its transmit power based on (e.g., inversely proportional to) the measured signal strength in order to mitigate interference to the WWAN UEs. In one design, the P2P UE may measure the signal strength of an uplink signal from a WWAN UE, estimate the pathloss between the two UEs based on the measured signal strength, and determine its transmit power based on the estimated pathloss.

The present application is a division of U.S. patent application Ser.No. 12/839,144 entitled “Mitigation of Interference Due to Peer to PeerCommunication filed on Jul. 19, 2010 which claims priority toprovisional U.S. Application Ser. No. 61/227,608, entitled “ADJACENTCHANNEL PROTECTION BY P2P DEVICES,” filed Jul. 22, 2009, both of whichare assigned to the assignee hereof and incorporated herein byreference.

BACKGROUND

I. Field

The present disclosure relates generally to communication, and morespecifically to techniques for mitigating interference in a wirelesscommunication network.

II. Background

Wireless communication networks are widely deployed to provide variouscommunication content such as voice, video, packet data, messaging,broadcast, etc. These wireless networks may be multiple-access networkscapable of supporting multiple users by sharing the available networkresources. Examples of such wireless networks include wireless wide areanetworks (WWANs) and wireless local area networks (WLANs).

A wireless communication network may include a number of base stationsthat can support communication for a number of user equipments (UEs). AUE may communicate with a base station via the downlink and uplink. Thedownlink (or forward link) refers to the communication link from thebase station to the UE, and the uplink (or reverse link) refers to thecommunication link from the UE to the base station.

A UE may also be able to communicate peer-to-peer (P2P) with another UE,without communicating with a base station in a wireless network. P2Pcommunication may reduce the load on the wireless network for localcommunication. Furthermore, P2P communication between two UEs may enablea first UE to act as a relay for a second UE. This may allow the secondUE to communicate with a wireless network even though the second UE maybe outside of the normal coverage of the wireless network. However, P2Pcommunication may cause interference to other UEs (or WWAN UEs)communicating with base stations in the wireless network. It may bedesirable to mitigate interference due to P2P communication on the WWANUEs.

SUMMARY

Techniques for mitigating interference due to P2P communication aredescribed herein. A P2P UE may communicate peer-to-peer with another UEand may transmit a downlink signal on a particular carrier. Thisdownlink signal may cause interference to WWAN UEs communicating withbase stations on the same carrier or a different carrier.

In an aspect, the P2P UE may measure the signal strength of downlinksignals from base stations on adjacent carriers and/or on its carrier.The P2P UE may set its transmit power based on (e.g., proportional to)the measured signal strength in order to mitigate interference to theWWAN UEs. If the measured signal strength is sufficiently strong, thenthe P2P UE may transmit at higher power since it may have lessinterference impact on the WWAN UEs. Conversely, if the measured signalstrength is low, then the P2P UE may transmit at lower power in order toreduce interference to the WWAN UEs.

In another aspect, the P2P UE may measure the signal strength of uplinksignals from WWAN UEs on adjacent carriers and/or on its carrier. TheP2P UE may set its transmit power based on (e.g., inversely proportionalto) the measured signal strength in order to mitigate interference tothe WWAN UEs. In one design, the P2P UE may measure the signal strengthof an uplink signal from a WWAN UE and may determine its transmit powerbased on the measured signal strength. In one design, the P2P UE mayestimate the pathloss between the WWAN UE and the P2P UE based on themeasured signal strength and a nominal/expected transmit power of theuplink signal. The P2P UE may then determine its transmit power based onthe estimated pathloss and a target received power of the downlinksignal from the P2P UE at the WWAN UE.

Various aspects and features of the disclosure are described in furtherdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication network.

FIG. 2 shows WWAN and P2P communications on different carriers.

FIG. 3 shows exemplary spectral mask requirements for a UE.

FIG. 4 shows operation of a P2P UE to mitigate interference to a WWANUE.

FIGS. 5 and 6 show a process and an apparatus, respectively, formitigating interference due to P2P communication based on measurement ofdownlink signals.

FIGS. 7 and 8 show a process and an apparatus, respectively, formitigating interference due to P2P communication based on measurement ofuplink signals.

FIG. 9 shows a block diagram of a P2P UE and a station.

DETAILED DESCRIPTION

The techniques described herein may be used for various wirelesscommunication networks such as WWANs, WLANs, etc. The terms “network”and “system” are often used interchangeably. A WWAN may be a CodeDivision Multiple Access (CDMA) network, a Time Division Multiple Access(TDMA) network, a Frequency Division Multiple Access (FDMA) network, anOrthogonal FDMA (OFDMA) network, a Single-Carrier FDMA (SC-FDMA)network, etc. A CDMA network may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. A TDMA network may implement aradio technology such as Global System for Mobile Communications (GSM).An OFDMA network may implement a radio technology such as Evolved UTRA(E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.16 (WiMAX), IEEE802.20, Flash-OFDM®, etc. UTRA and E-UTRA are part of Universal MobileTelecommunication System (UMTS). 3GPP Long Term Evolution (LTE) andLTE-Advanced (LTE-A) are new releases of UMTS that use E-UTRA. UTRA,E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from anorganization named “3rd Generation Partnership Project” (3GPP). cdma2000and UMB are described in documents from an organization named “3rdGeneration Partnership Project 2” (3GPP2). A WLAN may implement one ormore standards in the IEEE 802.11 family of standards (which is alsoreferred to as Wi-Fi), Hiperlan, etc. The techniques described hereinmay be used for the wireless networks and radio technologies mentionedabove as well as other wireless networks and radio technologies. Forclarity, much of the description below is for a WWAN.

FIG. 1 shows a wireless communication network 100, which may be a WWAN.Wireless network 100 may include a number of base stations and othernetwork entities that can support communication for a number of UEs. Forsimplicity, only one base station 110 and three UEs 120, 122 and 124 areshown in FIG. 1. Base station 110 may be an entity that communicateswith the UEs and may also be referred to as a Node B, an evolved Node B(eNB), an access point, etc. Base station 110 may provide communicationcoverage for a particular geographic area and may support communicationfor the UEs located within the coverage area. The term “cell” can referto a coverage area of base station 110 and/or a base station subsystemserving this coverage area.

UEs may be dispersed throughout the wireless network, and each UE may bestationary or mobile. A UE may also be referred to as a mobile station,a terminal, an access terminal, a subscriber unit, a station, etc. A UEmay be a cellular phone, a personal digital assistant (PDA), a wirelessmodem, a wireless communication device, a handheld device, a laptopcomputer, a cordless phone, a wireless local loop (WLL) station, a smartphone, a netbook, a smartbook, etc. A UE may communicate with a basestation. Alternatively or additionally, the UE may communicatepeer-to-peer with other UEs.

In the example shown in FIG. 1, UE 120 may communicate with base station110 and may be referred to as a WWAN UE. For WWAN communication betweenUE 120 and base station 110, UE 120 may receive a WWAN downlink signalfrom base station 110 and may transmit a WWAN uplink signal to basestation 110. UEs 122 and 124 may communicate peer-to-peer with oneanother and may be referred to as P2P UEs. For P2P communication betweenUEs 122 and 124, UE 122 may transmit a P2P downlink signal to peer UE124 and may receive a P2P uplink signal from peer UE 124.

P2P communication may be supported in various manners. For example, P2PUEs may operate on a separate frequency spectrum that is not used by awireless network. Alternatively, P2P UEs may utilize the frequencyspectrum for the uplink of a wireless network because there may be adisadvantage to using the frequency spectrum for the downlink of thewireless network. A P2P UE communicating on the downlink spectrum may beclose to a WWAN UE communicating with the wireless network. If thedownlink spectrum is used, then the P2P UE may cause high interferenceto the WWAN UE on the downlink, which may then result in the WWAN UEbeing unable to receive the downlink signals from the wireless network.

FIG. 2 shows WWAN communication and P2P communication on separate butadjacent carriers. A number of carriers may be available forcommunication. Each carrier may be associated with a specific centerfrequency and a specific bandwidth. The carriers may be defined to benon-overlapping in frequency.

In the example shown in FIG. 2, a carrier 212 may be used for WWANcommunication on the uplink of a wireless network and may be referred toas a WWAN uplink carrier. A carrier 222 may be used for WWANcommunication on the downlink of the wireless network and may bereferred to as a WWAN downlink carrier. A carrier 214 may be used forP2P communication on the uplink and may be referred to as a P2P uplinkcarrier. A carrier 224 may be used for P2P communication on the downlinkand may be referred to as a P2P downlink carrier.

Ideally, WWAN communication should be free of interference from P2Pcommunication, and vice versa. This may be achieved by using separatecarriers for WWAN communication and P2P communication, e.g., as shown inFIG. 2. This assumes that (i) WWAN communication can be constrained tobe completely within the WWAN downlink and uplink carriers and (ii) P2Pcommunication can be constrained to be completely within the P2Pdownlink and uplink carriers. However, this assumption typically doesnot hold.

FIG. 3 shows exemplary spectral mask requirements for a UE. A spectralmask may specify a certain maximum amount of ripple within a passbandand may require a certain minimum amount of attenuation in the stopband.A modulated signal transmitted by a UE may be required to conform to thespectral mask requirements. This modulated signal may include mostlydesired signal components in the passband and would typically includeundesired signal components in the stopband. The undesired signalcomponents may be at least Q decibels (dB) below the desired signalcomponents, where Q may be the required stopband attenuation.

The undesired signal components in the modulated signal from the UE mayresult from various phenomena such as local oscillator (LO) leakage,inphase/quadrature (I/Q) imbalance, and nonlinearity of a transmitter atthe UE. For example, LO leakage may result in a leaked LO signal at thecenter frequency, and this leaked LO signal may mix with the desiredsignal components to generate undesired signal components. I/Q imbalancemay result from gain error and/or phase error between the I and Q pathsin the transmitter and may generate undesired signal components.

As shown in FIG. 3, a P2P UE may cause interference on an adjacentcarrier due to out-of-band emissions from the P2P UE. This inter-carrierinterference may degrade the performance of a WWAN UE communicating witha wireless network on the adjacent carrier. From the wireless networkperspective, the inter-carrier interference may be more problematic thanintra-carrier interference caused by P2P UEs to WWAN UEs. This isbecause a base station may be able to take corrective actions tomitigate intra-carrier interference on its own carrier, e.g., bypartitioning the system bandwidth between the WWAN UEs and the P2P UEs.However, the base station may have little or no control on an adjacentcarrier. Hence, mechanisms to minimize inter-carrier interference fromP2P UEs to WWAN UEs on adjacent carrier may be highly desirable.

In an aspect, a P2P UE may detect for downlink signals from basestations on adjacent carriers and/or on its carrier and may measure thesignal strength of each carrier on which downlink signals are detected.Signal strength may correspond to received power or received signalquality. The P2P UE may set its transmit power based on (e.g.,proportional to) the measured signal strength. In particular, if themeasured signal strength is sufficiently strong, then the P2P UE maytransmit at higher power since it may have less interference impact onWWAN UEs communicating with the base stations. Conversely, if themeasured signal strength is low, then the P2P UE may transmit at lowerpower in order to reduce interference to the WWAN UEs.

The P2P UE may detect for downlink signals from base stations in variousmanners. In one design, the P2P UE may include a WWAN receiver for theradio technology used by the base stations. The P2P UE may then searchfor suitable transmissions or signals from the base stations using theWWAN receiver. For example, the P2P UE may search for (i)synchronization signals transmitted by the base stations to support cellsearch and acquisition by the WWAN UEs, (ii) reference signalstransmitted by the base stations to support channel estimation andchannel quality measurements by the WWAN UEs, and/or (iii) otherdownlink transmissions. A reference signal is a signal that is known apriori by a transmitter and a receiver and may also be referred to aspilot. The P2P UE may search for a cell-specific reference signal (CRS)transmitted by base stations in an LTE network, a common pilot channel(CPICH) transmitted by base stations in a WCDMA network, a pilot channel(PICH) transmitted by base stations in a CDMA 1X network, etc. The P2PUE may measure the signal strength of a detected signal (e.g., the CRS,CPICH, or PICH) on the carrier on which the signal is detected.Alternatively, the P2P UE may measure (i) the signal strength of othertransmissions and/or signals on the carrier or (ii) the signal strengthof the entire carrier.

In one design, the P2P UE may periodically detect for downlink signalsfrom base stations and may measure the signal strength of each carrieron which a downlink signal is detected. The P2P UE may perform signaldetection and measurement during measurement gaps, which may be gaps incommunication for the P2P UE. The measurement gaps may be (i) periods ofno communication defined by a radio technology to allow UEs to makemeasurements or (ii) periods in which the P2P UE is not communicating.

The P2P UE may determine its transmit power based on the measured signalstrength on adjacent carriers and/or on its carrier in various manners.In one design, the P2P UE may determine its transmit power based on afunction of the measured signal strength, as follows:P _(TX) =f(P _(RX)),  Eq (1)where P_(RX) is the measured signal strength, f(P_(RX)) may be anysuitable function, and P_(TX) is the transmit power of the P2P UE. Thefunction may be defined based on one or more other parameters besidesmeasured signal strength. In the description herein, transmit power andreceived power are given in units of decibel relative to one milli-Watt(dBm), and pathloss and offsets are given in units of dB.

In one design, the P2P UE may determine its transmit power based on themeasured signal strength, as follows:P _(TX) =P _(RX)+Δ_(OS),  Eq (2)where Δ_(OS) is an offset. The offset may be any suitable value that canprovide good performance for the P2P UE and the WWAN UEs.

In another design, the P2P UE may compare the measured signal strengthagainst different ranges of values, with each range being associatedwith a different transmit power for the P2P UE. The P2P UE may use thetransmit power for the range within which the measured signal strengthfalls.

In general, the P2P UE may transmit at progressively higher transmitpower for progressively higher measured signal strength. The transmitpower of the P2P UE may or may not be a linear function of the measuredsignal strength. In one design, the P2P UE may select a transmit powerthat is lower than the maximum transmit power if measurement of signalstrength on adjacent carriers and/or on its carrier is not successful.If a signal from a base station is not detected, then either a basestation is not present or is present but too weak to be detected. TheP2P UE may assume the latter and may restrict its transmit power to anupper bound in order to reduce impact to the operation of the basestation.

In another aspect, a P2P UE may measure the signal strength of uplinksignals from WWAN UEs on adjacent carriers and/or on its carrier. TheP2P UE may set its transmit power based on (e.g., inversely proportionalto) the measured signal strength in order to reduce interference to theWWAN UEs. The operation of the P2P UE may be more clearly described withthe following example.

FIG. 4 shows operation of a P2P UE to mitigate interference to a WWANUE. In the example shown in FIG. 4, the WWAN UE may communicate with abase station in a wireless network. The P2P UE may communicatepeer-to-peer with another UE, which may be referred to as the peer UE.

For WWAN communication, the WWAN UE may receive a WWAN downlink signalfrom the base station and may transmit a WWAN uplink signal to the basestation. For P2P communication, the P2P UE may transmit a P2P downlinksignal to the peer UE and may receive a P2P uplink signal from the peerUE. The P2P UE and the WWAN UE may be within close proximity of oneanother. The P2P UE may receive the WWAN uplink signal transmitted bythe WWAN UE to the base station. Correspondingly, the WWAN UE mayreceive the P2P downlink signal transmitted by the P2P UE to the peerUE. At the WWAN UE, the P2P downlink signal from the P2P UE may act asinterference to the WWAN downlink signal from the base station and maydegrade the performance of the WWAN UE.

The base station may transmit the WWAN downlink signal at a transmitpower of P_(TX,DL1). The WWAN UE may receive the WWAN downlink signal ata received power of P_(RX,DL1)=P_(TX,DL1)−X, where X is the pathlossfrom the base station to the WWAN UE. The WWAN UE may estimate thepathloss based on the known transmit power and the measured receivedpower of the WWAN downlink signal. The WWAN UE may transmit the WWANuplink signal at a transmit power of P_(TX,UL1), which may be expressedas:P _(TX,UL1) =P ₁ +X,  Eq (3)where P₁ is a target received power of the WWAN uplink signal at thebase station.

The P2P UE may receive the WWAN uplink signal at a received power ofP_(RX,UL1)=P_(TX,UL1)−Y, where Y is the pathloss from the WWAN UE to theP2P UE. The P2P UE may not know the transmit power of the WWAN uplinksignal and may estimate a “corrected” pathloss by assuming anominal/expected transmit power for the WWAN uplink signal, as follows:

$\begin{matrix}\begin{matrix}{Z = {P_{{TX},{{UL}\; 1},{NOM}} - P_{{RX},{{UL}\; 1}}}} \\{{= {P_{{TX},{{UL}\; 1},{NOM}} - \left( {P_{{TX},{{UL}\; 1}} - Y} \right)}},}\end{matrix} & {{Eq}\mspace{14mu}(4)}\end{matrix}$where P_(TX,UL1,NOM) is the nominal transmit power of the WWAN uplinksignal, and Z is the corrected pathloss.

The P2P UE may transmit the P2P downlink signal at a transmit power ofP_(TX,UL2), which may be expressed as:

$\begin{matrix}\begin{matrix}{P_{{TX},{{DL}\; 2}} = {P_{2} + Z}} \\{{= {P_{2} + P_{{TX},{{UL}\; 1},{NOM}} - \left( {P_{{TX},{{UL}\; 1}} - Y} \right)}},}\end{matrix} & {{Eq}\mspace{14mu}(5)}\end{matrix}$where P₂ is a target received power of the P2P downlink signal at theWWAN UE.

The WWAN UE may receive the P2P downlink signal at a received power ofP_(RX,DL2), which may be expressed as:

$\begin{matrix}\begin{matrix}{P_{{RX},{{DL}\; 2}} = {P_{{TX},{{DL}\; 2}} - Y}} \\{= {P_{2} + Z - Y}} \\{= {P_{2} + P_{{TX},{{UL}\; 1},{NOM}} - P_{1} - {X.}}}\end{matrix} & {{Eq}\mspace{14mu}(6)}\end{matrix}$

A signal-to-noise-and-interference ratio (SINR) of the WWAN downlinksignal at the WWAN UE may be expressed as:

$\begin{matrix}\begin{matrix}{{SINR} = {P_{{RX},{{DL}\; 1}} - P_{{RX},{{DL}\; 2}}}} \\{= {\left( {P_{{TX},{{DL}\; 1}} - X} \right) - \left( {P_{2} + P_{{TX},{{UL}\; 1},{NOM}} - P_{1} - X} \right)}} \\{= {\left( {P_{{TX},{{DL}\; 1}} - P_{{TX},{{UL}\; 1},{NOM}}} \right) + P_{1} - {P_{2}.}}}\end{matrix} & {{Eq}\mspace{14mu}(7)}\end{matrix}$

Equation (7) assumes that the pathloss from the WWAN UE to the P2P UE isapproximately equal to the pathloss from the P2P UE to the WWAN UE.Equation (7) also assumes that all or most of the interference observedby the WWAN UE comes from the P2P downlink signal from the P2P UE.

As an example, the transmit power, the received power, and the pathlossof various signals in FIG. 4 may have the following values:

For the WWAN downlink and uplink:

-   -   P_(TX,DL1)=+43 dBm, P_(RX,DL1)=−42 dBm, X=85 dB,    -   P_(TX,UL1)=−15 dBm, P₁=−100 dBm,

For the links between the WWAN UE and the P2P UE:

-   -   P_(TX,UL1)=−15 dBm, P_(RX,UL1)=−50 dBm, Y=35 dB,    -   P_(TX,UL1,NOM)=−10 dBm, P₂=−60 dBm, Z=40 dB,    -   P_(TX,DL2)=−20 dBm, P_(RX,DL2)=−55 dBm.

For the example given above, the base station may transmit the WWANdownlink signal at a transmit power of +43 dBm. The WWAN UE may receivethe WWAN downlink signal at a received power of −42 dBm with a pathlossof 85 dB. The target received power of the WWAN uplink signal at thebase station may be −100 dBm. The WWAN UE may transmit the WWAN uplinksignal at a transmit power of −15 dBm due to the 85 dB pathloss. Thepathloss from the WWAN UE to the P2P UE may be 35 dB, and the P2P UE mayreceive the WWAN uplink signal with a received power of −50 dBm. Thenominal/expected transmit power of the WWAN uplink signal may be −10dBm, and the corrected pathloss may be 40 dB. The target received powerof the P2P downlink signal at the WWAN UE may be −60 dBm, and the P2P UEmay transmit the P2P downlink signal at a power level of −20 dBm. Thereceived power of the P2P downlink signal at the WWAN UE may be −55 dBm.The SINR of the WWAN downlink signal at the WWAN UE may beSINR=−42+55=13 dB.

As shown in equation (7), the WWAN UE may observe an SINR that may beindependent of the locations of the WWAN UE and the P2P UE. Inparticular, the SINR is not dependent on the pathloss X of the WWANlinks or the pathloss Y of the P2P links. A target SINR for the WWAN UEmay be determined based on appropriate values for the parameters shownin the last line of equation (7). For example, P₂ may be selected toobtain the target SINR for the WWAN UE.

In the design show in equation (3), the WWAN UE may perform pathlossinversion and may set its transmit power proportional to the pathlossbetween the WWAN UE and the base station. In a second design, powercontrol may be used to adjust the transmit power of the WWAN UE. In thisdesign, the transmit power of the WWAN uplink signal from the WWAN UEmay be expressed as:P _(TX,UL1) =P ₁ +g(X),  Eq (8)where g(X) may be any suitable function of pathloss.

For the second design, the P2P UE may set its transmit power for its P2Pdownlink signal as described above for FIG. 4. The SINR of the WWAN UEmay then be expressed as:SINR=(P _(TX,DL1) −P _(TX,UL1,NOM))+P ₁ −P ₂ −X+g(X).  Eq (9)

For the second design, the SINR of the WWAN UE may be dependent on thepathloss X between the WWAN UE and the base station, which may in turnbe dependent on the location of the WWAN UE. A conservative estimate ofthe minimum possible value of g(X)−X may be used, and P₂ may be selectedto account for g(X)−X and to achieve the target SINR for the WWAN UE. P₂may also be selected to compensate for link imbalance between thedownlink and uplink, calibration errors, etc.

For clarity, the description above assumes that the P2P UE transmits theP2P downlink signal on the same carrier used by the base station totransmit the WWAN downlink signal. If the P2P UE and the base stationtransmit on adjacent carriers, then the transmit power of the P2Pdownlink signal may be determined as follows:

$\begin{matrix}\begin{matrix}{P_{{TX},{{DL}\; 2}} = {P_{2} + Z + \delta_{OS}}} \\{{= {P_{2} + P_{{TX},{{UL}\; 1},{NOM}} - \left( {P_{{TX},{{UL}\; 1}} - Y} \right) + \delta_{OS}}},}\end{matrix} & {{Eq}\mspace{14mu}(10)}\end{matrix}$where δ_(OS) is an offset or adjustment. The offset δ_(OS) may bedependent on the stopband attenuation requirements for the P2P UE. Forexample, if the stopband attenuation is 30 dB, then the offset may beequal to 30 dB. The transmit power of the P2P UE may then be increasedby 30 dB due to operation on an adjacent carrier instead of on the samecarrier as the base station.

In one design, the P2P UE may autonomously measure the received power ofthe WWAN uplink signal from the WWAN UE and may adjust its transmitpower for the P2P downlink signal based on the received power of theWWAN uplink signal to mitigate interference to the WWAN UE. The P2P UEmay be provided with the values of pertinent parameters to compute itstransmit power, e.g., as shown in equation (5) or (10). The WWAN UE andthe base station may not need to be aware of the presence of the P2P UE.In another design, the P2P UE may autonomously measure the totalreceived power on the uplink. This design may be used, e.g., when theP2P UE does not have information about the WWAN UE and is unable tomeasure the received power of the WWAN UE.

In another design, the P2P UE may be provided with information that maybe used to improve interference mitigation to the WWAN UE. For example,the P2P UE may be provided with information for one or more of thefollowing:

-   -   Transmit power used by the WWAN UE, which may replace the        nominal transmit power P_(TX,UL1,NOM), and    -   Sequences used by the WWAN UE, which may be used to search for        the WWAN uplink signal from the WWAN UE.

In one design, the P2P UE may perform interference mitigation all thetime for the WWAN UE. In another design, the P2P UE may performinterference mitigation whenever requested. For example, the WWAN UE mayobserve poor channel conditions on the WWAN downlink and may report thisto the base station. The base station may then transmit informationregarding the poor channel conditions observed by the WWAN UE. The P2PUE may receive the information from the base station and may performinterference mitigation in response to receiving the information.

FIG. 5 shows a design of a process 500 for mitigating interference dueto peer-to-peer communication. Process 500 may be performed by a UE (asdescribed below) or by some other entity. The UE may detect for adownlink signal from a base station based on at least onesynchronization signal, or at least one reference signal, and/or someother transmission or signal transmitted by the base station. The UE maycommunicate peer-to-peer with another UE and may not be communicatingwith the base station. The UE may measure the signal strength (e.g.,received power) of the downlink signal from the base station (block512). The UE may determine its transmit power based on the measuredsignal strength of the downlink signal (block 514). In one design, theUE may determine its transmit power based on a function of the measuredsignal strength of the downlink signal, e.g., as shown in equation (1).In another design, the UE may determine its transmit power based on themeasured signal strength of the downlink signal and an offset, e.g., asshown in equation (2).

The UE may receive the downlink signal from the base station on a firstcarrier. In one design, the UE may transmit on the first carrier and maydetermine its transmit power for this carrier. In another design, the UEmay transmit on a second carrier that is different from (e.g., adjacentto) the first carrier and may determine its transmit power for thesecond carrier.

FIG. 6 shows a design of an apparatus 600 for mitigating interferencedue to peer-to-peer communication. Apparatus 600 includes a module 612to measure signal strength of a downlink signal from a base station, anda module 614 to determine the transmit power of a UE based on themeasured signal strength of the downlink signal. The UE may communicatepeer-to-peer with another UE and may not be communicating with the basestation.

FIG. 7 shows a design of a process 700 for mitigating interference to afirst UE due to peer-to-peer communication by a second UE. The first UEmay communicate with a base station, and the second UE may communicatepeer-to-peer with a third UE. Process 700 may be performed by the secondUE (as described below) or by some other entity. The second UE maymeasure the signal strength (e.g., received power) of at least an uplinksignal from the first UE (block 712). In one design, the second UE maymeasure the signal strength of only the uplink signal from the first UE.In another design, the second UE may measure the total signal strengthon the uplink, which would include the uplink signal from the first UEand possibly uplink signals from other UEs. In either case, the secondUE may determine its transmit power based on the measured signalstrength of at least the uplink signal from the first UE (block 714).

The first UE may receive a downlink signal on a first carrier from thebase station. In one design, the second UE may transmit on the firstcarrier and may determine its transmit power for the first carrier basedon the measured signal strength of at least the uplink signal from thefirst UE. In another design, the second UE may transmit on a secondcarrier that is different from (e.g., adjacent to) the first carrier andmay determine its transmit power for the second carrier based on themeasured signal strength of at least the uplink signal from the firstUE.

In one design of block 714, the second UE may estimate the pathloss(e.g., Z) between the first UE and the second UE based on the measuredsignal strength (e.g., P_(RX,UL1)) of the uplink signal from the firstUE. The pathloss may be estimated based further on a nominal/expectedtransmit power (e.g., P_(TX,UL1,NOM)) of the uplink signal from thefirst UE, e.g., as shown in equation (4). The second UE may thendetermine its transmit power based on the estimated pathloss and atarget received power (e.g., P₂) of a downlink signal from the second UEat the first UE, e.g., as shown in equation (5). The second UE may alsodetermine its transmit power based further on an offset (e.g., δ_(OS)),which may be determined by an amount of attenuation of out-of-bandemission from the second UE, e.g., as shown in equation (10).

The target received power of the downlink signal from the second UE maybe selected to provide the desired performance for the first UE and topossibly account for other factors. In one design, the uplink signalfrom the first UE may be determined based on a function of pathlossbetween the first UE and a base station, e.g., as shown in equation (8).In this case, the target received power of the downlink signal from thesecond UE at the first UE may be determined based on the function ofpathloss.

In one design, the second UE may perform interference mitigation all thetime. In another design, the second UE may perform interferencemitigation only when requested or directed. In this design, the secondUE may receive information indicative of the first UE observing poorchannel conditions. In response, the second UE may determine itstransmit power based on the measured signal strength of the uplinksignal from the first UE to mitigate interference to the first UE.

In one design, the second UE may perform interference mitigationautonomously based on information known to and/or collected by thesecond UE. In another design, the second UE may receive informationrelated to the uplink signal transmitted by the first UE and may performinterference mitigation based on the received information. Thisinformation may be received from the first UE and/or the base stationcommunicating with the first UE. The second UE may measure the signalstrength of the uplink signal based on the received information, whichmay include information on sequences used by the first UE, etc. Thesecond UE may also determine its transmit power based on the receivedinformation, which may include the transmit power of the first UE, etc.

FIG. 8 shows a design of an apparatus 800 for mitigating interference toa first UE due to peer-to-peer communication by a second UE. Apparatus800 may be for the second UE. Apparatus 800 includes a module 812 tomeasure signal strength of at least an uplink signal from the first UEat the second UE, wherein the first UE communicates with a base stationand the second UE communicates peer-to-peer with a third UE, and amodule 814 to determine the transmit power of the second UE based on themeasured signal strength of at least the uplink signal from the firstUE.

The modules in FIGS. 6 and 8 may comprise processors, electronicdevices, hardware devices, electronic components, logical circuits,memories, software codes, firmware codes, etc., or any combinationthereof.

FIG. 9 shows a block diagram of a design of a station 112 and P2P UE122. Station 112 may be base station 110 or UE 120 in FIG. 1. Station112 may be equipped with T antennas 934 a through 934 t, and UE 122 maybe equipped with R antennas 952 a through 952 r, where in general T≧1and R≧1.

At station 112, a transmit processor 920 may receive data from a datasource 912 and control information from a controller/processor 940.Processor 920 may process (e.g., encode and modulate) the data andcontrol information to obtain data symbols and control symbols,respectively. Processor 920 may also generate reference symbols for oneor more reference signals and/or one or more synchronization signals. Atransmit (TX) multiple-input multiple-output (MIMO) processor 930 mayperform spatial processing (e.g., precoding) on the data symbols, thecontrol symbols, and/or the reference symbols, if applicable, and mayprovide T output symbol streams to T modulators (MODs) 932 a through 932t. Each modulator 932 may process a respective output symbol stream(e.g., for OFDM, SC-FDMA, etc.) to obtain an output sample stream. Eachmodulator 932 may further process (e.g., convert to analog, amplify,filter, and upconvert) the output sample stream to obtain a modulatedsignal. T modulated signals from modulators 932 a through 932 t may betransmitted via T antennas 934 a through 934 t, respectively.

At UE 122, antennas 952 a through 952 r may receive the modulatedsignals from station 112 and other stations (e.g., peer UE 124, otherUEs, and/or base stations) and may provide received signals todemodulators (DEMODs) 954 a through 954 r, respectively. Eachdemodulator 954 may condition (e.g., filter, amplify, downconvert, anddigitize) a respective received signal to obtain input samples. Eachdemodulator 954 may further process the input samples (e.g., for OFDM,SC-FDMA, etc.) to obtain received symbols. A MIMO detector 956 mayobtain received symbols from all R demodulators 954 a through 954 r,perform MIMO detection on the received symbols if applicable, andprovide detected symbols. A receive processor 958 may process (e.g.,demodulate and decode) the detected symbols, provide decoded data for UE122 to a data sink 960, and provide decoded control information to acontroller/processor 980.

At UE 122, a transmit processor 964 may receive data from a data source962 and control information from controller/processor 980. Processor 964may process (e.g., encode and modulate) the data and control informationto obtain data symbols and control symbols, respectively. Processor 964may also generate reference symbols for one or more reference signalsand/or one or more synchronization signals. The symbols from transmitprocessor 964 may be precoded by a TX MIMO processor 966 if applicable,further processed by modulators 954 a through 954 r (e.g., for SC-FDM,OFDM, etc.), and transmitted to peer UE 124 and/or other stations.Station 112 may receive the modulated signals transmitted by UE 122.

At station 112, the modulated signals from UE 122 and other stations(e.g., other UEs and/or base stations) may be received by antennas 934,processed by demodulators 932, detected by a MIMO detector 936 ifapplicable, and further processed by a receive processor 938 to obtaindecoded data and control information sent to station 112. Processor 938may provide the decoded data to a data sink 939 and the decoded controlinformation to controller/processor 940.

Controllers/processors 940 and 980 may direct the operation at station112 and UE 122, respectively. Memories 942 and 982 may store data andprogram codes for station 112 and UE 122, respectively. Demodulators 954and/or processor 980 may detect for signals from base stations and/orUEs and may measure the signal strength of the detected signals.Processor 980 may determine the transmit power of UE 122 based on themeasured signal strength, as described above. Processor 980 and/or otherprocessors and modules at UE 122 may perform or direct process 500 inFIG. 5, process 700 in FIG. 7, and/or other processes for the techniquesdescribed herein.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, computer software, or combinations of both. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method for wireless communication, comprising:measuring signal strength of at least an uplink signal from a first userequipment (UE) at a second UE, wherein the first UE communicates with abase station and the second UE communicates peer-to-peer with a thirdUE; and determining transmit power of the second UE based on themeasured signal strength of at least the uplink signal from the firstUE, wherein the determining the transmit power of the second UEcomprises estimating pathloss between the first UE and the second UEbased on the measured signal strength of the at least one uplink signalfrom the first UE, and determining the transmit power of the second UEbased on the estimated pathloss.
 2. The method of claim 1, wherein themeasuring the signal strength comprises measuring the signal strength ofonly the uplink signal from the first UE, and wherein the determiningthe transmit power of the second UE comprises determining the transmitpower of the second UE based on the measured signal strength of only theuplink signal from the first UE.
 3. The method of claim 2, wherein theestimating the pathloss between the first UE and the second UE based onthe measured signal strength of the at least one uplink signal from thefirst UE comprises estimating the pathloss between the first UE and thesecond UE based on the measured signal strength of only the uplinksignal from the first UE.
 4. The method of claim 3, wherein the pathlossbetween the first UE and the second UE is estimated based further on anominal transmit power of the uplink signal from the first UE.
 5. Themethod of claim 2, further comprising: receiving information related tothe uplink signal from the first UE, and wherein the signal strength ofonly the uplink signal from the first UE is measured based on thereceived information, or the transmit power of the second UE isdetermined based on the received information, or both.
 6. The method ofclaim 1, wherein the measuring the signal strength comprises measuringtotal signal strength of uplink at the second UE, and wherein thedetermining the transmit power of the second UE comprises determiningthe transmit power of the second UE based on the measured total signalstrength of the uplink.
 7. The method of claim 1, further comprising:receiving information indicative of the first UE observing poor channelconditions, and wherein the transmit power of the second UE isdetermined based on the measured signal strength of at least the uplinksignal from the first UE in response to receiving the information. 8.The method of claim 1, wherein the first UE receives a downlink signalon a first carrier from the base station, and wherein the transmit powerof the second UE on the first carrier is determined based on themeasured signal strength of at least the uplink signal from the firstUE.
 9. A method for wireless communication, comprising: measuring signalstrength of at least an uplink signal from a first user equipment (UE)at a second UE, wherein the first UE communicates with a base stationand the second UE communicates peer-to-peer with a third UE; anddetermining transmit power of the second UE based on the measured signalstrength of at least the uplink signal from the first UE, wherein thetransmit power of the second UE is determined based further on a targetreceived power of a downlink signal from the second UE at the first UE.10. The method of claim 9, wherein transmit power of the uplink signalfrom the first UE is determined based on a function of pathloss betweenthe first UE and a base station, and wherein the target received powerof the downlink signal from the second UE at the first UE is determinedbased on the function of pathloss.
 11. A method for wirelesscommunication, comprising: measuring signal strength of at least anuplink signal from a first user equipment (UE) at a second UE, whereinthe first UE communicates with a base station and the second UEcommunicates peer-to-peer with a third UE; and determining transmitpower of the second UE based on the measured signal strength of at leastthe uplink signal from the first UE, wherein the transmit power of thesecond UE is determined based further on an offset determined by anamount of attenuation of out-of-band emission from the second UE.
 12. Amethod for wireless communication, comprising: measuring signal strengthof at least an uplink signal from a first user equipment (UE) at asecond UE, wherein the first UE communicates with a base station and thesecond UE communicates peer-to-peer with a third UE; and determiningtransmit power of the second UE based on the measured signal strength ofat least the uplink signal from the first UE, wherein the first UEreceives a downlink signal on a first carrier from the base station, andwherein the transmit power of the second UE on a second carrier isdetermined based on the measured signal strength of at least the uplinksignal from the first UE, the second carrier being different from thefirst carrier.
 13. An apparatus for wireless communication, comprising:means for measuring signal strength of at least an uplink signal from afirst user equipment (UE) at a second UE, wherein the first UEcommunicates with a base station and the second UE communicatespeer-to-peer with a third UE; and means for determining transmit powerof the second UE based on the measured signal strength of at least theuplink signal from the first UE, wherein the means for determining thetransmit power of the second UE comprises: means for estimating pathlossbetween the first UE and the second UE based on the measured signalstrength of the at least one uplink signal from the first UE, and meansfor determining the transmit power of the second UE based on theestimated pathloss.
 14. The apparatus of claim 13, wherein the means formeasuring the signal strength comprises means for measuring the signalstrength of only the uplink signal from the first UE, and wherein themeans for determining the transmit power of the second UE comprisesmeans for determining the transmit power of the second UE based on themeasured signal strength of only the uplink signal from the first UE.15. The apparatus of claim 14, wherein the means for means forestimating pathloss between the first UE and the second UE based on themeasured signal strength of the at least one uplink signal from thefirst UE comprises: means for estimating pathloss between the first UEand the second UE based on the measured signal strength of only theuplink signal from the first UE.
 16. An apparatus for wirelesscommunication, comprising: means for measuring signal strength of atleast an uplink signal from a first user equipment (UE) at a second UE,wherein the first UE communicates with a base station and the second UEcommunicates peer-to-peer with a third UE; and means for determiningtransmit power of the second UE based on the measured signal strength ofat least the uplink signal from the first UE, wherein the transmit powerof the second UE is determined based further on a target received powerof a downlink signal from the second UE at the first UE.
 17. Anapparatus for wireless communication, comprising: means for measuringsignal strength of at least an uplink signal from a first user equipment(UE) at a second UE, wherein the first UE communicates with a basestation and the second UE communicates peer-to-peer with a third UE; andmeans for determining transmit power of the second UE based on themeasured signal strength of at least the uplink signal from the firstUE, wherein the transmit power of the second UE is determined basedfurther on an offset determined by an amount of attenuation ofout-of-band emission from the second UE.
 18. An apparatus for wirelesscommunication, comprising: means for measuring signal strength of atleast an uplink signal from a first user equipment (UE) at a second UE,wherein the first UE communicates with a base station and the second UEcommunicates peer-to-peer with a third UE; and means for determiningtransmit power of the second UE based on the measured signal strength ofat least the uplink signal from the first UE, wherein the first UEreceives a downlink signal on a first carrier from a base station, andwherein the transmit power of the second UE on a second carrier isdetermined based on the measured signal strength of at least the uplinksignal from the first UE, the second carrier being different from thefirst carrier.
 19. An apparatus for wireless communication, comprising:at least one processor configured to: measure signal strength of atleast an uplink signal from a first user equipment (UE) at a second UE;determine transmit power of the second UE based on the measured signalstrength of at least the uplink signal from the first UE, wherein thefirst UE communicates with a base station and the second UE communicatespeer-to-peer with a third UE; estimate pathloss between the first UE andthe second UE based on the measured signal strength of the at least oneuplink signal from the first UE; and determine the transmit power of thesecond UE based on the estimated pathloss.
 20. A computer programproduct, comprising: a non-transitory computer-readable mediumcomprising: code for causing at least one computer to measure signalstrength of at least an uplink signal from a first user equipment (UE)at a second UE, wherein the first UE communicates with a base stationand the second UE communicates peer-to-peer with a third UE; code forcausing the at least one computer to determine transmit power of thesecond UE based on the measured signal strength of at least the uplinksignal from the first UE; code for causing the at least one computer toestimate pathloss between the first UE and the second UE based on themeasured signal strength of the at least one uplink signal from thefirst UE; and code for causing the at least one computer to determinethe transmit power of the second UE based on the estimated pathloss.